1. Field of the Invention
The present invention relates to a slide bearing which supports a rotating shaft of a rotating machine such as a steam turbine by oil film pressure of lubricating oil.
2. Description of the Related Art
A slide bearing 100 as shown in FIG. 9 and FIGS. 10A and 10B is used in a rotating machine such as a steam turbine or a power generator to support a load of a rotating shaft. The slide bearing 100 includes a lower half bearing portion 101 and an upper half bearing portion 102, which can be joined together or split apart at an upper end face 103 of the lower half bearing portion 101 and a lower end face 104 of the upper half bearing portion 102.
The lower half bearing portion 101 has an oil supply groove 105 and an oil discharge groove 107 formed in the upper end face 103. When the rotating machine is in operation, lubricating oil is supplied to the oil supply groove 105 through an oil supply hole 106. The lubricating oil then spreads in an axial direction at the oil supply groove 105 and flows into clearance or gap between a rotating shaft 110 and an inner peripheral surface 109 of the lower half bearing portion 101.
Oil film pressure is created in the lubricating oil flowing into the clearance so as to support a load of the rotating shaft 110.
As the rotating shaft 110 rotates, the lubricating oil flows onto an inner peripheral surface 111 of the upper half bearing portion 102. Part of the lubricating oil passes through the oil discharge groove 107 and an oil discharge hole 108 and is discharged outside the slide bearing 100. The upper half bearing portion 102 has an overshot groove 112 formed in a part of the inner peripheral surface 111 in an axial direction. The overshot groove 112 is formed so as to intentionally increase clearance between the rotating shaft 110 and the inner peripheral surface 111 of the upper half bearing portion 102 so as to reduce friction losses caused by viscosity of the lubricating oil.
As shown in FIGS. 11 and 12, there has recently been proposed a slide bearing 115 which is obtained by reversing directions of oil supply and oil discharge by reversing positions of the oil supply hole 106 and oil discharge hole 108 and positions of the oil supply groove 105 and oil discharge groove 107 of the slide bearing 100, and additionally forming weirs 113 and 114 at portions of the inner peripheral surface 111 of the upper half bearing portion 102 that are left in front of and behind the overshot groove 112 such as disclosed in Patent Document 1 (Japanese Utility Model Laid-Open Publication No. 58-177621).
Clearance between the weirs 113 and 114 and the rotating shaft 110 is about 0.1 to 1 mm, which is smaller than depth of the overshot groove 112. For this reason, fluid resistance is produced at surfaces of the weirs 113 and 114. The amount of the lubricating oil flowing from the oil discharge groove 107 or oil supply groove 105 into the overshot groove 112 is smaller than that in the slide bearing 100 without forming the weirs 113 and 114.
As described above, according to such arrangement, the amount of the lubricating oil flowing into the overshot groove 112 upon rotation of the rotating shaft 110 can be reduced by reversing the directions of oil supply and oil discharge and providing the weirs 113 and 114. Therefore, since the lubricating oil can be prevented from remaining in the overshot groove 112, a reduction in friction losses caused by viscosity of the lubricating oil can be ensured.
Additionally, an discharge port 116 which causes the overshot groove 112 to communicate with an outside of the slide bearing 115 may be provided at a position rotationally upstream of the weir 114 on the slide bearing 115 side. In such case, a part of lubricating oil, having passed through the overshot groove 112 and risen in temperature, is stemmed by the weir 114 on the oil supply groove 105 side and is discharged outside the slide bearing 115 through the discharge port 116. Consequently, temperature of the lubricating oil flowing onto the inner peripheral surface 109 of the lower half bearing portion 101 can be kept low.
The slide bearing 100 shown in FIG. 9 and FIGS. 10A and 10B has been widely used for a conventional steam turbine generator of a steam power plant. In accordance with a recent increase in performance and output of steam turbines, the rotating shaft 110 heavy in weight must be sometimes adopted. In this case, the required amount of lubricating oil supplied to the slide bearing 100 tends to be large.
In contrast, the slide bearing 115 shown in FIG. 11 and FIGS. 12A and 12B can control the amount of the lubricating oil flowing into the overshot groove 112 and can actively supply the lubricating oil onto the inner peripheral surface 109 of the lower half bearing portion 101. Accordingly, even if the slide bearing 115 increases in size, the amount of the lubricating oil required to be supplied can be made smaller than that for the slide bearing 100.
For the reason described above, in a turbine changing period in an existing plant for the purpose of improving operational performance, it is advantageous for cost reduction and reduction in work period to change the slide bearing 100 to the slide bearing 115 because of usage of the existing oil supply facility such as an oil feeding header without substantive modification or alternation.
In the arrangement described above, however, since the slide bearing 100 and slide bearing 115 are opposite to each other in the positions of the oil supply hole 106 and oil discharge hole 108, routing of pipes connected to the holes 106 and 108 are made complicated and difficult at the time of bearing replacement in an existing plant.